Downhole fluid recirculation valve

ABSTRACT

A downhole valve for insertion in a production tubing string permits recirculation of fluid pumped into the casing annulus. The valve includes a cylindrical housing defining an opening, an internal mandrel disposed within the housing, defining a central bore and defining an opening, a valve between the housing and the mandrel, wherein said valve opens to allow fluid communication from the mandrel central bore to the annulus space in response to a pressure differential between the mandrel central bore and the annular space, and biasing means for biasing the valve in a closed position. The valve may be set within a completion string by wireline techniques

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 12/398,651 filed on Mar. 5, 2009 entitled “Downhole FluidRecirculation Valve”, the contents of which are incorporated herein byreference.

FIELD OF INVENTION

The present invention relates to a fluid recirculation valve, and moreparticularly to a downhole gas recirculation valve used in wellcompletions.

BACKGROUND

A well completion refers to the process of making an oil or gas wellready for production. Generally, this process involves running inproduction tubing, and perforating or stimulating as required.

Some gas producing wells use plungers to lift production gas and liquidsto the surface by providing a seal within the production tubing andutilizing downhole pressure to lift the plunger. In some cases, aplunger lift may be enhanced by increasing downhole pressure. In arelatively non-porous formation, gas or fluid may be injected into thecasing-tubing annulus, which in turn returns up through the productiontubing. However, in such techniques cannot be used in more porousformations as the fluid will be lost into the formation.

It is known to provide means for recirculating fluid from the annularspace through to the production tubing, however such means haveinvariably involved a check valve which forms part of the tubing string.The disadvantage to this completion is the check valve is permanent andcannot be serviced. Once the useful lift of this valve is reached itmust be disabled with the use of a tubing patch or an expensive wellre-completion.

Therefore, there is a need in the art for an improved downhole valvewhich permits one way flow of fluids from the annular space to thetubing string while mitigating the disadvantages of the prior art.

SUMMARY OF INVENTION

The present invention relates to a gas recirculation valve which may beinstalled during a well completion and which is installed through theproduction tubing. As a result, installation, removal and servicing maybe accomplished without expensive re-completions. This valve alsoprovides a means for retrieval and servicing via wireline intervention.

In one aspect, the invention may comprise a downhole valve for insertionin a production tubing string and a casing string, wherein an annularspace is defined between the tubing and the casing, said valvecomprising:

-   -   (a) a cylindrical housing defining an opening;    -   (b) an internal mandrel disposed within the housing, defining a        central bore and defining an opening;    -   (c) a valve disposed between the housing and the mandrel,        wherein said valve is moveable between an open position which        allows fluid communication from the mandrel central bore to the        annular space through the housing opening and the mandrel        opening, wherein said valve is responsive to a pressure        differential between the mandrel central bore and the annular        space; and    -   (d) a spring for biasing the valve in a closed position.

In another aspect, the invention may comprise a method of recirculatingfluid in a well comprising a production tubing string and a casingstring, wherein an annular space is defined between the tubing and thecasing, said method comprising the steps of:

-   -   (a) installing a downhole fluid recirculation valve into a        completion string which forms part of the production tubing        string, wherein said valve is disposed between two packoffs        isolating a valve zone between them, said valve zone is in fluid        communication with the annular space;    -   (b) installing isolation means for isolating the annular space        below the isolation means from the annular space above the        isolation means; and    -   (c) pumping fluid under pressure into the annular space such        that the valve opens and the fluid passes into the production        tubing string and returns to the surface.

The recirculating gas may be used to drive an intermitting plunger inthe production tubing string or it may be used to maintain a critical orminimum gas flow rate in the tubing.

In another aspect, the invention comprises a method of setting adownhole fluid recirculation valve within a completion string,comprising the steps of placing a completion string comprising a tubingsliding sleeve within a wellbore, setting an upper packoff and a lowerpackoff to define a valve zone, running the valve within the completionstring to a position within the valve zone by a wireline.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments are illustrated in referenced figures of thedrawings. It is intended that the embodiments and figures disclosedherein are to be considered illustrative rather than restrictive.

FIG. 1 is a schematic disclosing the different sections of a well-bore.

FIG. 2 is a schematic of the upper section of a well-bore disclosed inFIG. 1.

FIG. 3 is a schematic of the flow control section of a well-boredisclosed in FIG. 1.

FIG. 4 is a schematic of the lower section of the well-bore disclosed inFIG. 1.

FIG. 5 is a schematic of the well-bore perforation section disclosed inFIG. 1.

FIG. 6 is a perspective view of an embodiment of the current invention.

FIG. 7 is a schematic of the free flow control valve of the invention inan open position with the spring in a compressed state.

FIG. 8 is a schematic of the free flow control valve of the invention ina closed position with the spring in a relaxed state. FIG. 8A shows adetail of the pressure equalization chamber.

DETAILED DESCRIPTION

The present invention relates to a method and apparatus forrecirculating fluids in a wellbore having an annular space between acasing string and a tubing string. When describing the presentinvention, all terms not defined herein have their common art-recognizedmeanings. To the extent that the following description is of a specificembodiment or a particular use of the invention, it is intended to beillustrative only, and not limiting of the claimed invention. Thefollowing description is intended to cover all alternatives,modifications and equivalents that are included in the spirit and scopeof the invention, as defined in the appended claims.

In one embodiment, the valve (10) described herein is a completion toolwhich is part of a completion string, as shown in FIG. 1. The followingdescription is of one embodiment of the tool and its use in a gasre-circulation completion.

As shown in FIGS. 1 and 2, the valve (10) is installed as part of acompletion string which includes an upper section (A) having a landingspring (12) for an intermitter (14), such as an intermitter described inApplicant's co-owned U.S. Pat. No. 7,188,670. As is well known in theart, the intermitter (14) travels up and down within the productiontubing (1), pushing up accumulated well fluids to the surface. It isurged upward by pressure within the production tubing, below theintermitter (14).

The various components of the completion string are well known in theart, and are not intended to be limiting of the valve of the presentinvention, unless specifically claimed in that manner.

The valve (10) is run into the flow control section (B) between twowireline conveyed tubing packoffs (16, 18). The upper velocity tubepackoff (16) may be located in upper section (A). The lower section (C)includes the lower velocity tube packoff (18) and the velocity tubeanchor (20). The upper and lower packoffs (16, 18) isolate the valvezone within the production tubing. The lower velocity tube (22) hangsfrom the velocity tube anchor (20) and ends with a velocity tubeisolation valve (28) in the perforation section (D). The lower velocitytube (22) passes through the tubing packoff (26) which isolates theannular space from the perforation section (D).

The production tubing (1) is in selective fluid communication with theannular space by means of perforations or a sliding sleeve (19) whichcan be opened or closed. The perforations or sliding sleeve open up thetubing in the valve zone between the upper and lower packoffs (16, 18).The valve (10) resides in the valve zone, and may be is run in insidethe sliding sleeve (19) on an upper velocity tube (23).

Thus fluid communication between the annulus and the production tubing,above the tubing packoff (26) is controlled by the sliding sleeve (19)and the valve (10).

In one embodiment, the valve (10) may be installed above the slidingsleeve (19) rather than the configuration shown in FIG. 3, where thevalve (10) is disposed below the sliding sleeve (19).

Produced fluids from the perforation section enters the tubing (1)through the isolation valve (28) into the lower velocity tube (22),passes through the valve (10), and upwards through the upper velocitytube (23) and into the production tubing.

The valve (10) permits one-way flow of fluids from the annular spacebetween the tubing (1) and the casing (2), above the tubing packoff(26), into the tubing. Gas or liquid introduced into the annular spaceis isolated from the perforation section (D) by the tubing packoff (26).As a result, such gas or liquid will return to the surface by enteringthe tubing through the valve (10). Thus, the tubing below theintermitter may be pressurized by injecting fluids into the annularspace and through the valve (10).

As shown in FIGS. 6 and 7, the valve (10) itself includes a housing(50), and a mandrel (52) concentrically disposed within the housing(50). The mandrel is attached to a top sub (54) which allows threadedconnection to the remainder of the completion string, which may be runinto the production tubing by conventional wireline techniques. At thelower end of the valve (10), the mandrel (52) engages the inner surfaceof the housing. An O-ring (56) provides a seal between the mandrel andthe housing at the lower end.

The housing (50) engages a piston sub (58) which connects to the top sub(54), which connection is sealed with O-ring (61).

The housing (50) defines a plurality of openings (60) which arepreferably covered by a filter screen (62). The openings provide fluidcommunication from outside the housing (50) to a space (51) between thehousing and the mandrel. Within the space (51) between the housing andthe mandrel, a cylindrical member fits in close tolerance to the outsidediameter of the mandrel and acts as a valve (64). In FIG. 8, the valve(64) is shown in its closed position, where the lower end of the valvemember (64) is seated against a shoulder (66) formed on the inside ofthe housing, and against a shoulder (68) formed on the outside of themandrel. In its open position, as shown in FIG. 7, the valve member (64)slides upwards and opens a fluid passageway between the two shoulders(66, 68). The mandrel defines a number of openings (70) immediatelyabove shoulder (68) which become exposed when the valve member (64)travels upwards and opens.

Therefore, when the valve member (64) is in its open position, a fluidpassageway is created from the annular space, through housing openings(60), between shoulders (66, 68) and through mandrel openings (70), andinto the production tubing through the interior of the valve (10).

When there is no pressure differential between the annulus and theinternal bore of the mandrel, the valve member (64) is normallymaintained in its lowered, closed position by coil spring (72) which isdisposed in the same space between the housing and the mandrel. Theupper end of the spring (72) bears on a spacer (74) while the lower endof the spring bears on the valve member (64). As is apparent, thecompression of the spring (72) may be overcome by a pressuredifferential between the annular space, and the production tubing. Suchfluid pressure urges the valve member (64) to its open position byovercoming the force of the spring (72). The force of the spring (72) onthe valve (64), and therefore the pressure differential required to openthe valve, may be varied by varying the strength of the spring or byincreasing or decreasing the size of spacer (74).

In one embodiment, a valve extension piston (76) is attached to theupper end of the valve (64) and extends upwards between the spring (72)and the mandrel (52), and further extends past the spacer (74) and anisolation ring (78) which provides a seal with both the housing and themandrel through the use of O-rings. The upper end of the valve extensionpiston (76) reciprocates within a pressure equalization chamber (80)which is in fluid communication with the production tubing by way ofopenings (82) in the mandrel. The upper end of the valve extensionpiston (76) does not cover the openings (82) to the equalization chamber(80). Therefore, the pressure equalization chamber (80) is always at thesame pressure as that within the production tubing. At the same time, alower portion of the pressure equalization chamber is open to theannular space through openings (83).

The upper end (84) of the valve extension piston slides along the insideof the pressure equalization chamber (80) and includes an O-ring seal(86). In one embodiment, it is preferred to have a highly polishedsurface inside the pressure equalization chamber (80) to limit thefriction of the O-ring seal (86) and ensure the movement of the valveextension piston (76) is relatively unimpeded.

When fluid pressure in the annulus is higher than in the tubing, thepressure equalization chamber (80) utilizes the static pressuredifferential to help maintain the valve in a constant full open state.This system dampens the effect of the gas flow pressure fluctuationsinduced by the expansion and contraction of the gas moving through thelower end of the valve (10).

An entry guide (88) encircles the housing at its lower end, and providesa chamfered sub to facilitate running the tools inside the tubing.

In operation, fluid such as a gas may be pumped downhole through theannulus, creating a pressure differential between the annulus and theproduction tubing. As a result, the valve (10) will open and allow fluidto flow into the production tubing. If an intermitter is installed, theintroduced gas will assist in lifting the intermitter to the surface.When the pressure differential equalizes, the valve (10) will close.

1. A method of setting a downhole fluid recirculation valve within acompletion string, comprising the steps of placing a completion stringcomprising a tubing sliding sleeve within a wellbore, setting an upperpackoff and a lower packoff to define a valve zone, running the valvewithin the completion string to a position within the valve zone by awireline.
 2. The method of claim 1 wherein the valve comprises: (a) acylindrical housing defining an opening; (b) an internal mandreldisposed within the housing, defining a central bore and defining anopening; (c) a valve disposed between the housing and the mandrel,wherein said valve is moveable between an open position which allowsfluid communication from the mandrel central bore through the housingopening and the mandrel opening, wherein said valve is responsive to apressure differential between the mandrel central bore and the valveenvironment; and (d) a spring for biasing the valve in a closedposition, wherein the spring comprises a coil spring concentricallydisposed within the housing, and around the mandrel.
 3. The method ofclaim 2 wherein the valve comprises a sliding member having a sealingportion at its distal end, wherein said sealing portion covers themandrel opening when the valve is in its closed position.
 4. The methodof claim 3 wherein the sliding member is a cylindrical memberconcentrically disposed within the housing and around the mandrel. 5.The method of claim 4 wherein the spring comprises a coil springconcentrically disposed within the housing, and around the mandrel. 6.The method of claim 2 wherein the valve further comprises a pressureequalization chamber formed between the housing and the mandrel, a firstportion of which is in fluid communication with the mandrel inner bore,and a second portion of which is in fluid communication with theannulus, and further comprising a valve extension piston which engagesthe upper end of the valve which comprises an upper end whichreciprocates in the pressure equalization chamber between the first andsecond portions.